Similar-sized women who exercised regularly but maintained their usual calorie intake did not post big drops in pounds or in those suspect proteins, reports the Fred Hutch study, published recently inCancer Research, a journal of the American Association for Cancer Research.

“The fact that exercise alone had little effect was … surprising,” said Catherine Duggan, study co-leader and principal staff scientist in the Public Health Sciences Division at the Hutch.

“Many people still think they just need to exercise a little more and they’ll lose a lot of weight. Doesn’t happen,” said Anne McTiernan, the article’s senior author and a cancer prevention researcher at the Hutch.

The scales of the women studied revealed the power of portion over perspiration:

Women who followed the weight-loss diet—a daily calorie goal based on starting weight and a reduction of fat to less than 30 percent of total calories—lost, on average, 8.5 percent of their starting weight after one year.

Those who followed that diet while exercising moderately to vigorously for 45 minutes a day, five days a week lost, on average, a bit more—10.8 percent of their weight after a year.

But those who stuck to that exercise plan while not curtailing their calories lost, on average, only 2.4 percent of their weight when the year had elapsed. (Most women will not gain a significant amount of muscle mass with exercise, said McTiernan.)

The study enrolled 439 women from the Seattle area who were randomly placed into one of four groups—exercise only, diet only, exercise plus diet or no change to health habits. The women were aged 50 to 75, sedentary, postmenopausal, and either overweight or obese but otherwise healthy.

“We know that being overweight and having a sedentary lifestyle is associated with an increase in risk for developing certain kinds of cancer. However, we don’t know exactly why,” Duggan said.

That’s where the three proteins examined by Duggan and McTiernan may offer clues.

Blood samples were collected from the study participants at the trial’s start. In each of those samples, researchers measured three proteins—VEGF, PAI-1 and PEDF—that flow through the body and help in the formation of new blood vessels, a process called angiogenesis.

That mechanism can boost the body in tiny or crucial ways, such as amid wound healing. But angiogenesis—a sprouting of fresh blood vessels to carry oxygen and nutrients—also occurs during the growth of tumors. The three measured proteins are involved in nurturing the growth and survival of cancer cells.

The women who adhered for one year to the caloric restriction and lower-fat eating—or a combination of the diet and workout plans—had significantly decreased levels of those angiogenesis-related proteins, the study found.

Those same women met regularly with dietitians who helped them infuse their menus and dining habits with more fruits and vegetables, better portion control, daily weighing and food journaling.

Lower levels of the cancer-associated proteins were not found in the women who participated in the exercise-only group, the study showed.

The Hutch researchers cannot currently say that when someone loses weight and lowers their levels of angiogenic-related proteins it definitively decreases that person’s likelihood of a cancer diagnosis.

But the findings do add to a growing body of evidence showing the link between being overweight and having elevated levels of certain proteins associated with a higher cancer risk, Duggan said.